Re: [PATCH 2/3] evaluate: allow to use string with binary operations

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Tue, Jan 14, 2014 at 12:22:52PM +0000, Patrick McHardy wrote:
> On Tue, Jan 14, 2014 at 12:30:29PM +0100, Pablo Neira Ayuso wrote:
> > This allows us to match ifname masks, eg.
> > 
> > nft add rule filter output meta oifname and eth == eth counter
> > 
> > I've been investigating other possibility, such as adding
> > ofiname-mask, which requires several patches and transformations
> > to make it look binop tree, but I still think this looks like
> > a natural way (and simple, look at the patch, it's rather small)
> > to represent this in the nftables.
> 
> I was just going to suggest adding a shortcut for this since its exposing
> a lot of low-level detail. The transformation should be quite easy during
> evaluation, could you elaborate on the problems?

Not really a problem but a bit more specific code to handle this case.
I started writing support for this following several approaches, but
after looking at my patchset I thought this approach was smaller and
it's requiring way less specific code.

The fist of my patches here (the ones that I didn't send) replace all
NFT_META_* references in the parser by internal META_*, eg. META_MARK,
just to prepare the addition of META_IIFNAMEMASK and META_OIFNAMEMASK.
Then, the follow-up patch transforms the following expression that we
got from that looks like:

              relational
                /     \
               /       \
    meta oifnamemask  string

to a binary op expression. These also needs some specific code in the
delinearize path to transform the binop tree back to the expression
above.

Let me know if you have any better idea. Thanks.